WASHINGTON - A visibly distraught father of a 6-year-old killed at Sandy Hook Elementary School in Connecticut urged a Senate panel on Wednesday to pass legislation to prevent another gun massacre.

"It's hard for me to talk about my deceased son," said Neil Heslin, father of Jesse Lewis. "I'm not here for sympathy or a pat on the back. I'm here to speak up for my son."

Heslin broke down repeatedly, sobbing and pausing as he told the story of that fateful day on Dec. 14 when Jesse and 19 of his schoolmates died in Newtown, Conn. Heslin held a framed portrait of himself holding Jesse when he was a baby, as he pleaded with the Senate Judiciary Committee.

Heslin was a featured witness at the panel's first hearing on a bill to ban assault weapons, sponsored by Sen. Dianne Feinstein, D-Calif. The measure faces an uphill battle in Congress, attracting opposition from Democrats and Republicans alike.

Feinstein cited massacres that occurred at a Tucson grocery store, Virginia Tech University, a movie theater in Aurora, Colo., and the Newtown school to make her case.

"Weapons are more lethal today than they were in 2004," Feinstein said at a Senate Judicary Committee hearing on her proposal. "The need for a federal ban has never been greater."

Republican Sen. Chuck Grassley of Iowa, the ranking member on the Judiciary panel, repeated his opposition to Feinstein's bill, saying it was based on "arbitrary distinctions" and have "nothing to do with the functions of the weapons."

"Those arbitrary distinctions and the fact that these weapons are commonly used for self-defense raise constitutional questions under the Second Amendment," he said. "And the same questions of self-defense arise concerning magazines that enable firing of more than 10 rounds."

President Obama has called on Congress to set aside differences and ignore pressure from gun-rights groups such as the NRA. In addition to the assault weapons ban, Obama is seeking legislation that would mandate a universal background check for gun owners and a limit on the ammunition in magazine clips.

Feinstein's proposal would ban the future sales of assault weapons and magazines carrying more than 10 rounds of ammunition, but it would exempt those that already exist. The legislation would also bar the sales, manufacture and importation of semi-automatic rifles that can use detachable magazines and have certain military features. Specifically, 157 weapons would be banned but Feinstein said more than 2,200 others used for hunting and sport would be excluded.

While many Republicans in the GOP-controlled House are opposing an assault weapons ban, so are some of Feinstein's fellow Democrats who hail from red states, such as Arkansas Sen. Mark Pryor. He is one of several Democrats from states with high gun-ownership rates who is up for re-election in 2014.

The first assault weapons ban, signed into law by President Bill Clinton in 1994, expired in 2004. That ban only applied to weapons that were manufactured after its enactment. Congress has tried several times to renew the law, only to face stiff opposition in the House.

The hearing at one point became heated, as Sen. Lindsey Graham, R-S.C., and Milwaukee Police Chief Edward Flynn argued over background checks for gun owners. As Flynn began to explain the department's focus on prosecuting criminals rather than people who fail to pass federal background checks, Graham interrupted.

"It's clear that your focus is not on prosecuting people who fail background checks, would you agree with that?" Graham said, interrupting again to tell Flynn that he was frustrated that proponents of universally extending the checks don't recognize that current laws are not being enforced.